Photoelectrophoretic imaging apparatus employing photosensitive particles exhibiting fatigue characteristics

ABSTRACT

AN ELECTROPHORETIC IMAGING SYSTEM COMPRISING EXPOSING A SUSPENSION OF ELECTRICALLY PHOTOSENSITIVE PARTICLES IN A LIQUID CARRIER TO IMAGEWISE LIGHT AND, SUBSEQUENTLY, DEVELOPING THE IMAGE BY APPLYING A FIELD ACROSS THE SUSPENSION WHICH CAUSES PARTICLE MIGRATION IN IMAGE CONFIGURATION. THE PHOTOSENSITIVE PARTICLES OF THIS SYSTEM EXHIBIT FATIGUE CHARACTERISTICS IN THAT THEY REMAIN ELECTRICALLY SENSITIVE FOR A PERIOD OF TIME AFTER HAVING BEEN EXPOSED TO ACTIVATING ELECTROMAGNETIC RADIATION.   D R A W I N G

Feb. 29, 1972 LUEBBE, JR ET AL 3,645,883

PHOTOELECTROPHORETIC IMAGING APPARATUS EMPLOYING PHOTOSENSITIVEPARTICLES EXHIBITING FATIGUE CHARACTERISTICS Filed June 1, 1970 I m 1 I?FIGQ 1 FIG. 2

INVENTOR.

RAY H. LUEBBE JR. LEONARD M. CARREIRA A T TORNE Y United States PatentPHOTOELECTROPHORETIC IMAGING APPARA- TUS EMPLOYING PHOTOSENSITIVEPARTICLES EXHIBITING FATIGUE CHARACTERISTICS Ray H. Luebbe, Jr.,Rochester, and Leonard M. Carreira,

Penfield, N.Y., assignors to Xerox Corporation, Stamford, Conn.

Filed June 1, 1970, Ser. No. 42,409 Int. Cl. B01d 13/02 US. Cl. 204300 2Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Thisinvention relates in general to imaging systems and, more specifically,to improved electrophoretic imaging systems. This application is adivisional application of our copending application Ser. No. 675,864filed Oct. 17, 1967.

An electrophoretic imaging system has recently been developed capable ofproducing colored images which utilizes electrically photosensitiveparticles. This process is described in detail and claimed in copendingapplications Ser. Nos. 384,737 new :Pat. No. 3,384,565; 384,681 and384,680 both now abandoned all filed July 23, 1964. In such an imagingsystem, variously colored light absorbing particles are suspended in anon-conductive liquid carrier. The suspension is placed betweenelectrodes subjected to a potential diiference and exposed to an image.When these steps are completed, selective particle migration takes placein image configuration providing a visible image at one or both of theelectrodes. In a monochromatic system, particles of a single color maybe used producing a single colored image analogous to conventional blackand white photography. In a polychromatic system, natural color imagescan be produced by using mixtures of particles of two or more differentcolors which are each sensitive only to light of a specific wavelengthor narrow range of wavelengths.

In order to obtain images of, optimum quality, the potential appliedacross the imaging suspension between the electrodes is conventionallyon the order of several thousand volts. This high potential ismaintained between a pair of electrodes one of which is conductivecalled the injecting electrode and the other of which has an insulatingsurface backed by a conductive core called the blocking electrode.Ordinarily, one of these electrodes is transparent and the image to bereproduced is projected onto the imaging suspension through saidtransparent electrode. The electrodes are brought into contact with thesuspension while the potential is imposed between them during exposure.

The prior art process as described above produces high quality colorimages. However, several disadvantages are apparent in the prior artprocess. For example, in the prior art process, it was necessary to havefield applied during the imaging exposure. It was, therefore,conventional to use a transparent conductive electrode which was atleast as large as the desired image. Conductive transparent materialsare expensive and usually fragile. In addition, it was not possible tosequentially image and then to develop the resulting image.

SUM-MARY OF THE INVENTION It is, therefore, an object of this inventionto provide an electrophoretic imaging system and apparatus thereforewhich overcomes the above-noted disadvantages.

It is another object of this invention to provide an electrophoreticsequential imaging system and apparatus therefore capable of producingrelatively high quality images.

It is another object of this invention to provide an electrophoreticimaging system and apparatus which does not require the use ofrelatively large conductive transparent electrodes.

It is another object of this invention to provide an electrophoreticimaging system and apparatus wherein field application is not requiredduring the imaging step.

It is another object of this invention to provide a relatively simplenon-complex electrophoretic imaging system and apparatus.

The foregoing objects and others are accomplished in accordance withthis invention by providing an electrophoretic imaging system wherein animaging suspension of electrically photosenstive particles in a liquidcarrier is exposed to activating electromagnetic radiation and anelectrical field causing imagewise particle migration. The electricallyphotosensitive particles of this invention, will after having beenexposed to light, respond to subsequent application of electric field.In operation, the suspension is exposed to a pattern of activatingelectromagnetic radiation. The suspension is subsequently subjected toan electric field which causes imagewise particle migration.

In the prior art, imagewise exposure of the imaging suspension wascarried on simultaneously with application of field. The electric fieldwas applied simultaneously through conductive electrodes or was presentas an electrostatic charge on the surface of insulating members broughtin contact with the imaging suspension. Heretofore, it was possible todevelop images, that is, for particle migration to take place, only ifthe imagewise activating exposure and the field were presentsimultaneously. It has been learned that imaging suspension may beprepared wherein simultaneous field and light exposure is not required.It is possible to expose such an imaging suspension to activatingelectromagnetic radiation and then subsequently develop the image byexposure to a uniform electric field. The amount of time which canelapse between exposure to activating radiation and the developing stepdepends largely on the imaging suspension used, the

amount of exposure used, and the developing field strength.

The characteristic of particles in an imaging suspension which allowsdevelopment subsequent to imagewise exposure is referred to as fatigue.Whether a particular imaging suspension exhibits fatigue characteristicscannot be predicted. However, one skilled in the art may easilydetermine this characteristic by using an apparatus similar to thatshown in FIG. 1. The apparatus is described in detail later. In general,the experiment is performed as follows: An imaging suspension is coatedon the conductive surface of a NESA glass plate and exposed to imagewiseactivating electromagnetic radiation. Imagewise exposure is thendiscontinued. The charged developing electrode is then rolled across thesuspension providing an image on the conductive surface of, for example,a NESA glass plate. The time interval between discontinuance of thelight exposure and the termination of image formation on the surface ofthe NESA glass is defined as the fatigue characteristic for theparticular imaging suspension. The fatigue characteristic for aparticular suspension may be determined under various operatingconditions by varying the amount of exposure that the imaging suspensionis exposed to an also by varying the strength of the field across theimaging suspension during the developing step. The amount of time whichcan elapse between discontinuance of the exposure and image formation onthe surface of the NESA plate may vary from a few hundredths of a secondto hours.

For those particles having a fatigue characteristic of less than aboutone second, the embodiment of FIG. 1 should be modified to eliminate thedelay entailed in moving the roller blocking electrode to the injectingelectrode. 'Instead, so that field may be applied shortly afterimagewise exposure has been terminated, the blocking electrode should'be in the shape of a flat plate and should be placed on the imagingsuspension before imagewise exposure.

The exact mechanism of fatigue is not fully understood. In general,however, fatigue is that property of a material which allows thematerial to remain conductive or at least responsive to field for arelatively long period of time after it has been exposed to activatingelectromagnetic radiation. Materials which do not exhibit fatigue returnto an insulating or non-responsive state immediately after terminationof activating exposure.

Conventionally, the image formed on the surface of the injectingelectrode, here, the conductive transparent electrode, is transferred toa receiving sheet and fixed thereon for further use and viewing.However, since a negative image is formed on one of the electrodes and apositive image is formed on the other, it is possible to use eitherimage. The image may be fixed in place by spraying a binder on it,laminating an overlay on it, or by including a binder in solution in theliquid suspending medium. The image is preferably transferred from theelectrode and fixed on another surface so that the electrode may bereused. Such a transfer step may be carried out by adhesive pickoif withan adhesive tape such as Scotch Brand Cellophane Tape or preferably, byelectrostatic field transfer. Electrostatic transfer may, for example becarried out by carrying out the imaging procedure described and thenpassing a second roller over the particle image formed on the injectingelectrode holding the second roller at a potential opposite in polarityto that of the first electrode. If the transfer roller is covered with apaper sleeve, this paper will pick up the complete image as theelectrode rolls over the injecting electrode. -In addition, theparticles may include a component that may be made tacky by theapplication of heat or a properly selected solvent so that either ofthese can be used to adhere and fix the particle image to the electrodeor to a transfer surface.

The surface of the blocking electrode and the transfer electrode may beof any suitable insulating material. Typical materials are Baryta paper,cellulose acetate, polyethylene coated paper, cellophane, nitrocellulose, polystyrene, polytetrafluoroethylene, polyvinylfiuoride,polyethylene terephthalate, and mixtures thereof.

In the embodiment of this invention wherein imagewise exposure isprojected through one of the electrodes, any suitable transparentconductive electrode material may be used. Typical conductivetransparent electrode materials include: conductively coated glass suchas tin or indium oxide coated glass, aluminum coated glass, or similarcoatings on plastic substrates. NESA is preferred because of its hightransparency and inertness to the imaging suspension.

Both electrodes, however, may be made of any conductive electrodematerial and may be opaque. Typical conductive electrode materialsinclude: metal surfaces such as aluminum, brass, stainless steel,copper, nickel, zinc, etc., conductively coated glass, such as tin orindium oxide coated glass, aluminum coated glass, similar coatings onplastic substrates, rubber rendered conductive by inclusion of asuitable material therein, or paper rendered conductive by inclusion ofa suitable chemical therein, or through conditioning in a humidatmosphere to insure the presence therein of sufiicient water content torender the material conductive.

The charging, or developing, step described above may be performed byany conventional means, for example, by corona discharge as described inU.S. Pat. 2,588,699 to Carlson or U.S. Pat. 2,777,577 to Walkup. It ispreferred to use a charged blocking electrode as described previouslybecause the particles which migrate are removed from the systemimmediately providing a higher quality image on both electrodes. It isalso possible to use uniform light exposure to, in effect, activate theimaging suspension and then use imagewise field to provide a visibleimage. The imagewise field could, for example, be formed by a shapedelectrode or an insulator having on its surface an electrostatic latentimage.

Any suitable highly colored electrically photosensitive particle ormixtures of such particles may be used in carrying out the invention,regardless of Whether the particular particle selected is organic,inorganic and is made up of one or more components in solid solution ordispersed one in the other or whether the particles are made up ofmultiple layers of different materials or are combinations ofphotosensitive and non-photosensitive materials. Highly coloredelectrically photosensitive particles include organics such as8,13-dioxodinaphtho-(2,1-b;2',3-d)-furan- 6-carbox-p-methoxyanilide;Locarno Red, C.I. No. 15865, 1 (4 methyl-5'-chloroaZobenzene-2-sulfonicacid)-2- hydroxy-3-naphthoic acid; Watchung Red B, the barium salt of 1(4' methyl 5'-chloroazobenzene-2'-sulfonic acid) 2 hydroxy 3 naphthoicacid, C.I. No. 15865, Naphthol Red B,l-(2-methoxy-5'-nitrophenylazo)-2-hydroxy-3"-nitro-3-naphthanilide, C.I.No. 12355; Duol Carmine, the calcium lake of 1-(4'-methylazobenzene-2'-sulfonic acid) 2 hydroxy-3-naphthoic acid, C.I. No. 15850; CalciumLithol Red, the calcium lake of 1-(2'- azonaphthalene 1' sulfonicacid)-2-naphthol, C.I. No. 15630; Pyranthrones; Indofast BrilliantScarlet Toner, 3,4,9,10 bis(N,N' (p methoxy-phenyl)-imido)perylene, C.I.No. 71140; dichloro thioindigo; Pyrazolone Red B Toner, C.I. No. 21120;Methyl Violet, a phosphotungstomolybdic acid lake of a Triphenylmethanedye, C.I. 42535; Indofast Violet lake, dichloro-9,18-isoviolanthrone,C.I. No. 60010; Diane Blue, 3,3'-methoxy-4,4-diphenylbis(1 azo 2"hydroxy-3"-naphthanilide), C.I. No. 21180; Indanthrene Brillant OrangeR.K., 4,10-dibromo- 6,12-anthanthrone, C.I. No. 59300; Algol YellowG.C., 1,2,5,6 di(C,C' diphenyl)-thiazole-anthraquinone, C.I. No. 67300;Flavanthrone; Indofast Orange Toner, C.I. No. 71105; 1 cyano2,3-phthaloyl-7,8-benzopyrrocoline and many other thio indigos,acetoacetic arylides, anthraquinones, perinones, perylenes, dioxazines,quinacridones, azos, diazos, thoazines, azines and the like; inorganicssuch as cadmium sulfide, cadmium sulfoselenide, zinc oxide, zincsulfide, sulphur selenium, mercuric sulfide, lead oxide, lead sulfide,cadmium selenide titanium dioxide, indium trioxide and the like. Inaddition to the aforementioned pigments, other typical organic materialsInclude polyvinyl carbazole;

2,4-bis( 4,4-diethyl-aminophenyl) -1, 3 ,4-oxidiazole;

N-isopropylcarbazole;

polyvinyl-anthracene;

triphenylpyrrol;

4,S-diphenylimidazolidinone;

4,5-diphenylimidazolidinethione;

4,5 -bis- 4'-aminophenyl -irnidazolidinone;

1,2,5,6-tetraaza cyclooctatetraene- (2,4,6,8)

3,4di-(4'-methoxyphenyl) -7,8-diphenyl- 1 ,2,5,6-

tetraaza cyclooctatetraene- (2,4, 6, 8)

3,4-di(4-phenyoxyphenyl) -7,8-diphenyl-1,2,5,6-

tetraaza cyelooctateraene-(2,4,6,8);

3,4,7,8-tetramethoxy-l,2,5,6-tetraaza-cyclooctatetraene-Z-mercapto-benzthiazole;

2-phenyl-4-alpha-nuphthylidene-oxazolone;

Z-phenyl-4-diphenylidene-oxazolone;

2-phenyl-4-p-methoxybenzylidene-oxazolone;

6-hydroxy-2-phenyl- (p-dimethyl-amino phenyl) -benzofurane;

6-hydroxy-2,3-di- (p-methoxyphenyl) -benzofurance;

2,3,5 ,6-tetra- (p-methoxy-phenyl) -furo- (13,2f

benzofurane;

4-dimethyl-amino benzylidene-benzhydrazide;

4-dimethyl-aminobenzylideneiso-nicotinic acid hydrazide;

turfurylidene- (2) -4'-dimethylamino-b enzhydrazide;

S-benzilidene-amino-acenaphthene-3 -benzylidene-aminocarbazole;

(4,N,N-dimethylamino-benzylidene) -p-N,N-dimethylaminoaniline;

( 2-nitro-benzylidene) -p-bromo-aniline;

N,N-dimethyl-N'-(2-nitro-4-cyano-benzylidene) -pphenylene-diamine;

2,4-diphenyl-quinazoline;

2- (4'-amino-phenyl) -4-phenyl-quinazoline;

2-phenyl-4-(4-dimethyl-amino-phenyl) -7-methoxyquinazoline;

l,3-diphenyl-tetrahydroimidazole;

1, 3-di- (4'- chlorophenyl -tetrahydroimidazole;

l,3-diphenyl-2-4'-dimethyl aminophenyl) tetrahydroimidazole;

1,3-di- (p-tolyl-2- [quinolyl- (2-( ]-tetrahydromidazole;

2-(4'-di-methylamino-phenyl -5- (4"-methoxy-phenyl) 6-phenyl-l,2,4-triazine;

3-pyridil- (4 -5- (4"-dimethylaminophenyl) -6-phenyl- 1,2,4-triazine;

3-(4'-amino-phenyl)-5,6-di-phenyl-1,2,4-triazine;

2,5-[bis-4'-amino-phenyl-(1) ]-1,3,3-triazole;

2,5-bis [4'- (N-ethyl-N-acetyl-amino) -phenyll 1,3,4-tn'azole;

1,5 -diphenyl-3-methyl-pyrazoline;

1,3,4,S-tetraphenyl-pyrazoline;

1-phenyl-3- (p-methoxy-styrl) -5- (p-methoxy-phenyl pyrazoline;

1-methyl-2- 3,4'-dihydroxy-methylene-phenyl) benzimidazole;

2- (4'-dimethylamino-phenyl) -benzoxazole;

2- (4-methoxyphenyl -benzthiazole;

2,5-bis [p-amino-phenyl- 1 -I,'3,4-oxidiazole;

4,5-diphenyl-imidazolone;

3-amino-carbazole;

copolymers and mixtures thereof.

Other materials include organic donor-acceptor (Lew1s acid-Lewis base)charge transfer complexes made up of donors such as phenolaldehyderesins, phenoxies, epoxies, polycarbonates, urethanes, styrene or thelike complexed with electron acceptors such as2,4,7-trinitro-9-fluoroenone; 2,4,5,7 tetranitro-9-fluorenone; picricacid; 1,3,5- trinitro benzene; chloranil; 2,5-dichlorobenzoquinone;anthraquinone-Z-carboxylic acid, Bromal, 4-nitro-phenol; maleicanhydride; metal halides of the metals and metalloids of Groups I-B andIIVIII of the Periodic Table including for example, aluminum chloride,zinc chloride, ferric chloride, magnesium chloride, calcium iodide,strontium bromide, chromic bromide, arsenic triiodide, magnesiumbromide, stannous chloride, etc.; boron halides, such as borontrifluorides, ketones such as benzophenone and anisil, mineral acidssuch as sulfuric acid; organic carboxylic acids such as acetic acid andmaleic acid, succinic acid, citroconic acid, sulphonic acid, such as4-toluene sulphonic acid and mixtures thereof. In addition to the chargetransfer complexes it is to noted that many additional ones of the abovematerial may be further sensitized by the charge transfer complexingtechnique and that many of these materials may be dry-sensitized tonorrow, broaden or heighten their spectral response curves.

Quinacridones are preferred because of their high fatigue characteristicand excellent color. Any quinacridone, if suitable, may be used toprepare the imaging suspension of the present invention. Quinacridonesare compounds having a structure which appears to be the condensationproduct of a quinoline residue with an acridine residue with two carbonsof the condensation product oxidized to the quinone state. Anycrystalline phase may be used if suitable. The quinacridonse may besubstituted or unsubstituted.

Typical quinacridones include: 2,9 dimethyl-quinacridone; 3,10 dichloro6,13 dihydro-quinacridone; 2,9 dimethoxy 6,13 dihydro-quinacridone; 2,9dimethyl 6,13 dihydro-quinacridone; 4,11 dimethyl- 6,13dihydro-quinacridone; 3,4,10,11 tetrachloro-quinacridone; 2,4,9,11tetrachloro quinacridone; 2,4,9,11- tetrabromo quinacridone; 1,4,8,l1tetrafluoro quinacridone; 1,2,4,8,9,1l hexachloroquinacridone; 2,4,9,ll-tetramethoxy-quinacridone; and mixtures thereof. In addition, angularquinacridones, such as are disclosed in US. Pat. 2,830,990, may be usedWhere suitable.

2,9 dimethyl-quinacridone, available as quindo magenta RV6803 fromHarmon Colors, is preferred because of its high fatigue, excellentelectrical response and pure color.

Any suitable particle structure may be employed. Typical particlesinclude those which are made up of only the pure photosensitive materialor a sensitized form thereof, solid solutions or dispersions of thephotosensitive material in a matrix such as thermoplastic orthermosetting resins, copolymers of photosensitive pigments and organicmonomers, multilayers of particles in which the photosensitive materialis included in one of the layers and where outer layers provide lightfiltering action in an outer layer or a fusible or solvent softenablecore of resin or a core of liquid such as dye or other marking materialor a core of one photosensitive material coated with an overlayer ofanother photosensitive material to achieve broadened spectral response.Other photosensitive structures include solutions, dispersions, orcopolymers of one photosensitive material in another with or withoutother photosensitively inert materials. Other particle structuresinclude those described in US. Pat. 2,940,847 to Kaprelian.

Although various electrode spacings may be employed, spacings of lessthan 1 mil and extending down even to the point where the electrodes arepressed together as in the case of the roller electrode of FIG. 1constitute a particularly preferred form of the invention in that theyproduce better resolution and superior color separation results than isproduced with wider spacings. This improvement is believed to take placebecause of the high field strength across the suspension duringdevelopment.

Where a monochromatic image is to be formed, the particles will bepreferably of a single color. Where polychromatic images are to beformed, particles of two or more colors may be used. For example, forsubtractive color formation, the particles will ordinarily be magenta,cyan and yellow.

Any suitable insulating liquid may be used as a carrier for thephotosensitive particles and the imaging suspension. Typical insulatingcarrier liquids include: decane, dodecane, molten paraffin, moltenbeeswax, or other molten thermoplastic materials, Sohio Odorless Solvent3440 (a kerosene extraction available from Standard Oil Company ofOhio), Isopar G (a long chain saturated aliphatic hydrocarbon availablefrom Humble Oil Company of New Jersey) and mixtures thereof. Sohio ispreferred because it is a good insulator and evaporates readily.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages of this improved methodof imaging will become apparent upon consideration of the detaileddisclosure of the invention especially when taken in conjunction withthe accompanying drawings wherein:

FIG. 1 is a side sectional view which schematically shows an exemplaryimaging system.

FIG. 2 is a side sectional view which shows schematically an exemplaryimaging system which does not utilize a large transparent, conductiveelectrode.

Referring now to FIG. 1, there is shown an exemplary embodiment of anapparatus for forming a photoelectrophoretic image in accordance withthis invention. FIG. 1 shows transparent conductive electrode, generallydesignated 1, which in this exemplary instance is made up of a layer ofoptically transparent glass 2 overcoated with a thin opticallytransparent layer 3 of tin oxide commercially available under the nameNESA glass. This electrode shall hereafter be referred to as theinjecting electrode. Coated on the surface of injecting electrode 1 is athin layer 4 of finely divided photosensitive particles which exhibit afatigue characteristic dispersed in an insulating liquid carrier. Theterm fatigue for the purposes of the application, refers to thatproperty of a particle which once attracted to the injecting electrodewill allow the particle to migrate away from it under the influence ofan applied electric field at some time interval after it has beenexposed to actinic electromagnetic radiation. Adjacent to the liquidsuspension 4 is a second electrode 5 hereinafter referred to as theblocking electrode which is connected to one side of a potential source6 through a switch 7. The opposite side of potential source 6 isconnected to ground as is injecting electrode 1 so that when switch 7 isclosed an electric field is applied across the liquid suspension 4between electrodes 1 and 5.

The process operates as follows: imaging layer 4 is exposed to imagewiseactivating electromagnetic radiation 9. The activating exposure may beeither full frame or partial frame. More than one exposure may be used.In the case where more than one exposure is used, the exposures may besimultaneous or sequential. The amount of time which can elapse betweenthe initial imagewise exposure and the developing, or charging, step forsequential imaging depends on the fatigue characteristic for theelectrode 5 is rolled across the surface of the injecting particularimaging layer. The time which elapses between the initial imagewiseexposure and the development of the image must not exceed the fatiguecharacteristic for the particular imaging suspension. The imagewiseexposures may be, for example, light projected through a transparency orlight information projected from opaque subjects.

After imagewise exposure or exposures are completed, switch 7 is closedand blocking electrode generally designated 5 which is shaped in theform of a roller, comprising a conductive central core 11 which iscovered with a layer of a blocking material 12 which may be baryta paperor suitable material, is then rolled across the imaging suspensionlayer. The application of field between electrode 5 and electrode 1causes particles to migrate through the carrier liquid and adhere to thesurface of the blocking electrode 5 leaving behind a pigment image onthe injecting electrode surface which is a duplicate of the imagewiseexposure or combination of exposures that the suselectrode 1.)Preferably, the particulate image formed on the surface of injectingelectrode 1 is transferred to a receiving sheet and fixed thereon forfurther use or viewing. As described in copending application Ser. No.542,050, filed Apr. 2, 1966, in the US. Patent Oflice, a transfer rollermay be utilized to receive the image from the injecting electrodesurface. conventionally, a potential is imposed on the transfer roller,which normally is structurally identical with the blocking electrode,which is opposite in sign to that used on the blocking electrode duringthe developing step. Normally, during the transfer step the image areasare light exposed either to white light or to suitably filtered whitelight. Where desired, the surface of the particulate image on theinjecting electrode may be moistened with additional carrier liquid toimprove the transfer step.

Referring now to FIG. 2, there is shown an exemplary embodiment of asystem for forming a photoelectrophoretic image on one of the electrodeswhich does not require the use of a transparent conductive electrode. InFIG. 2, there is shown a blocking electrode generally designated 21which comprises a conductive plate 22 which in this exemplary instanceis aluminum, which has placed on its surface a film 23 of Tedlar (apolyvinyl fluoride available from du Pont) A thin layer 24 of finelydivided photosensitive particles which exhibit a memory effect dispersedin an insulating liquid carrier is then coated on sheet 23. Adjacent tothe liquid suspension 24 is a second electrode generally designated 25hereinafter called the injecting electrode which is connected to oneside of a potential source 26 through a switch 27. The opposite side ofpotential 26 is connected to ground as is blocking electrode 21 so thatwhen switch 27 is closed, an electric field is applied across the liquidsuspension 24 between electrodes 25 and 21.

The process is operated as follows: imaging suspension 24 is exposed toimagewise activating electromagnetic radiation in a manner similar tothat of FIG. 1 with the exception that here the exposure need not beprojected through either electrode. After termination of the imagewiseexposure injecting electrode 25 which comprises a conductive centralcore 31 covered with a sheet of conductive paper 32 is rolled across thesurface of the Tedlar sheet while field is applied. Application of fieldcauses particles to migrate in image configuration providing a visibleimage on both electrodes. The particulate image may be fixed in place orthe paper may be removed from the conductive core and the image fixedthereon or the image may be transferred to another member and fixedthereon for further use or viewing. The image may be transferred bypressure or electrostatically.

DESCRIPTION OF THE PREFERRED EMBODIMENTS- The following examples furtherspecifically illustrate the present invention. The examples below areintended to illustrate various preferred embodiments of the improvedimaging method. The parts and percentages are by weight unless otherwiseindicated.

EXAMPLE I In all of the examples which follow, the imaging suspension isheld in the dark for at least 30 minutes before imagewise illuminationof the suspension. grams of Naphthol Red B, C.I. No. 12355, availablefrom American Cyanamid (code 20-7575), is dissolved in reagent gradeethylenediamine in a closed container. The solution is filtered througha covered funnel and the filtrate poured into reagent grade isopropanol.The suspension thus formed is centrifuged in capped bottles. The pigmentis then Washed with an isopropanol-de-ionized water mixture. The pigmentis then washed with dimethylformamide followed by methanol washing. Thepigment is then dried.

About 8 parts of the purified Naphthol Red B is then suspended in 92parts of Sohio Odorless Solvent 3440, a kerosene fraction available fromStandard Oil of Ohio.

The suspension prepared above is then used in an apparatus of thegeneral type illustrated in FIG. 1 with the suspension coated on a NESAglass substrate through which exposure is made. The NESA glass surfaceis connected in series with a switch, a potential source, and theconductive center of a roller having baryta paper on its surface. Theroller is approximately 2 /2 inches in diameter and is moved across theplate surface at about 2 inches per second. The plate employed isapproximately 3 inches square and is exposed with a light intensity ofabout 960 foot-candles as measured on the uncoated NESA glass surface.The magnitude of the potential applied between the two electrodes isabout 3500 volts. The negative terminal is connected to the roller. Theexposure is made with a 3200 K. lamp through a transparency. Imagewiseillumination is continued for 5 seconds. Exposure is then terminated.The roller is then rolled across the surface of the suspension withpotential applied. An image, consisting of pigment particles, is founddeposited on the surface of the NESA glass, with a complimentary imagebeing formed on the baryta paper surface.

EXAMPLE II About 8 parts Naphthol Red M. C.I. No. 12390, available fromAmerican Cyanamid (code 20-7515), purified as was the Naphthol Red B ofExample I is suspended in 92 parts of Sohio 3440.

The suspension is tested in the apparatus of Example I using the sameconditions as in Example I except that imagewise illumination is made onthe free surface of the imaging suspension as shown in FIG. 2. An image,consisting of pigment particles is found deposited on the surface of theNESA glass with a complementary image being formed on the blockingelectrode surface.

EXAMPLE III About 8 parts of quindo magenta RV 6803, a 2,9-dimethylquinacridoue as obtained from Harmon Colors is suspended in about 92parts of Sohio Odorless Solvent 3440.

The suspension is tested in the apparatus of Example I using theexposure arrangement of Example II with the following exception:imagewise exposure of about 1000 foot-candles for about one second isused. An image is formed on the surface of the NESA glass and the barytapaper.

EXAMPLE IV The experiment of Example III is repeated except that afterthe first imagewise exposure has been terminated imagewise illuminationis made through a second transparency, approximately 10 seconds afterthe first imagewise illumination. The second imagewise illumination isalso of approximately 1000 foot-candle-seconds total exposure. An imageconforming to a combination of the two imagewise illuminations is foundformed on the surface of the NESA glass, a complementary image is formedon the baryta paper surface.

EXAMPLE V The experiment of Example IV is repeated except that fourimagewise illuminations of approximately 1000 footcandle-seconds eachare made at about second intervals. An image conforming to a combinationof the four imagewise illuminations is found formed on the surface ofthe NESA glass, a complementary image is formed on the baryta paper.

EXAMPLE VI Approximately 4 parts of quindo magenta are suspended inapproximately parts Sohio. The suspension is then used in an apparatusof the general type illustrated in FIG. 2. The suspension is coated on 2mil Tedlar, a polyvinylfiuoride film available from du Pont, which isplaced on the approximately 3 inch square by inch thick aluminum plate.The aluminum plate is connected in series with a switch, a potentialsource and the conductive center of a roller having a 2 mil thick sheetof cellophane on its surface. The roller is approximately 2 inches indiameter and is moved across the surface of the Tedlar at a rate ofabout 2 inches per second. The magnitude of the potential applied isabout 3500 volts with the positive terminal connected to the roller.Imagewise illumination of approximately 1000 foot-candles is made as inExample I with the exception that the exposure is directed onto thesuspension directly as shown in FIG. 2. After an exposure of about onesecond the imagewise illumination is discontinued and the roller isrolled across the suspension with potential applied. An image consistingof migrated pigment particles is found deposited on the surface of thecellophane, a complementary image is formed on the opposite electrode.

EXAMPLE VII The experiment of Example V is repeated except that fourimagewise illuminations of approximately 1000 footcandle-seconds eachare made at about 15 second intervals. An image conforming to acombination of the four imagewise illuminations is found formed on thesurface of the cellophane sheet, a complementary image is formed on theopposite electrode.

Although specific components and proportions have been stated in theabove description of preferred embodiments of the invention, othertypical materials as listed above if suitable may be used with similarresults. In addition, other materials may be added to the suspension tosynergize, enhance, or otherwise modify the properties of the imaginglayer. For example, a plastic component could be added to the suspensionwhich on evaporation of the carrier liquid would coat the final imagesproduced.

Other modifications and ramifications of the present invention willoccur to those skilled in the art upon a reading of the presentdisclosure. These are intended to be included within the scope of thisinvention.

What is claimed is:

1. A photoelectrophoretic imaging apparatus comprising an opaque firstelectrode supporting a photoelectrophoretic liquid imaging suspensionhaving fatigue characteristics, means to expose the free surface of saidsuspension to a pattern of electromagnetic radiation, means for applyingan electrical field across said suspension, a second opaque electrodefor contacting said suspension, and means for moving said secondelectrode into and out of contact with said suspension to form an image.

2. The apparatus of claim 1 wherein said opaque second electrode is aroller electrode having an insulating surface and further includingmeans for rolling said roller over said imaging suspension duringexposure.

References Cited UNITED STATES PATENTS 5/1968 Clark 204l8l 2/1969Mihajlov 204-300 US. Cl. X.R.

